Secretory Immunoglobulins: The ultrastructure of canine secretory component and J-chain are being investigated now that they have been isolated and purified from secretory IgA; the combination of these chains with 7S IgA monomer may elucidate the assembly of the secretory IgA molecule. Peyer's Patch Lymphocytes: While investigating the origin of precursor cells that differentiate into immunoglobulin secreting plasma lymphocyte cells in the gastrointestinal tract, the interactions of orally administered antigens and processing cells (T-lymphocytes) in gut-associated lymphoid tissue (Peyer's patches) were studies in adult guinea pigs. A detailed identification of the lymphoid cell populations in Peyer's patches and an assessment of lymphocyte activity (afferent and efferent T-cell functions) was made.